The present invention relates to a hydraulic servo mechanism for controlling a movable swash plate of a hydraulic continuously variable transmission of swash plate type composed by fluid coupling between a hydraulic pump and a hydraulic motor.
Hitherto, in a hydraulic continuously variable transmission composed of a hydraulic pump and a hydraulic motor, for example, the hydraulic pump is composed in a variable displacement type, and the displacement of the hydraulic pump is adjusted by controlling the slant angle of movable swash plate of the hydraulic pump by way of a hydraulic servo mechanism provided in the hydraulic continuously variable transmission.
This servo mechanism is manipulated by an operation lever attached to the outside of the hydraulic continuously variable transmission. This operation lever is, when the hydraulic continuously variable transmission is employed, for example, in a mobile vehicle, coupled and linked to a running speed change lever to be manually manipulated by the driver disposed in the cabin of the vehicle by means of a link mechanism or the like. The movable swash plate is coupled to a hydraulic piston of the hydraulic servo mechanism, and a spool as a hydraulic valve for controlling the supply of pressure fluid to both hydraulic chambers at both sides of the hydraulic piston is moved by manipulating the operation lever.
However, together with the operation lever, a neutral position holding mechanism, which holds a spool operating part at a position corresponding to a neutral position of the movable swash plate so as to hold the movable swash plate at the neutral position, a rotation limiting mechanism, which limits the move of the spool operating part so as to define the maximum rotating angle of the movable swash plate, and an over-stroke absorbing mechanism, which is constituted on a pivot portion of the operation lever so as to absorb the over-stroke of the operation lever manipulated beyond the moving limit of the spool operating, are disposed outside of the hydraulic continuously variable transmission. Therefore, in such configuration, various troubles were experienced, such as malfunction due to mud, dust or foreign matter sticking to the constituent members of these mechanisms, or deviation of adjustment due to impact from outside. Besides, together with the hydraulic continuously variable transmission, spaces for disposing these mechanisms are needed, and as a result the equipment is increased in size, it is hard to keep space for installation, and the cost is higher.
Further, some of the conventional hydraulic servo mechanisms for control of movable swash plate position comprise, aside from the manual hydraulic control mechanism for operating the spool by the operation lever as mentioned above, also an automatic hydraulic control mechanism as a solenoid valve for supplying pressure fluid to both hydraulic chambers at both sides of the piston.
The piston and the both pressure chambers are usually disposed in the vertical direction at a side of hydraulic pump or hydraulic motor having a movable swash plate coupled to the piston, and the solenoid valve is also disposed above or beneath the housing portion for enclosing the both hydraulic chambers, and therefore the entire equipment is large in size. Further, it required a considerable hydraulic pressure in order to drive the piston hydraulically by supplying pressure fluid directly into the both hydraulic chambers at both sides of the piston without passing through the spool as mentioned above, and an exclusive solenoid valve of a corresponding large capacity was used, which also added to the cost.
The hydraulic continuously variable transmission of the invention comprises a hydraulic servo mechanism for controlling the swash plate angle disposed within its body housing, and a manual operation member for operating the hydraulic servo mechanism disposed outside of the body housing, wherein a casing is provided between the manual operation member and the body housing, and wherein a neutral position holding mechanism for holding the neutral position of a movable swash plate and a rotation control mechanism for controlling the maximum rotating angle of the movable swash plate are installed in the casing. Further, an over-stroke absorbing mechanism for absorbing the over-stroke of the manual operation member is installed in an area ranging from the inside of the casing to the inside of the body housing.
In this configuration, the constituent members of the neutral position holding mechanism, rotation control mechanism and over-stroke absorbing mechanism are protected by the casing or body housing, and are not contaminated by mud, dust or foreign matter, and occurrence of malfunction or deviation of adjustment due to impact from outside can be prevented. Each mechanism can be designed in a small size, and the cost can be reduced.
Also in this configuration, the hydraulic servo mechanism has a spool as a hydraulic valve, and a spool operating member moving from the inside of the casing to the inside of the body housing by operation of the manual operation member is disposed movably almost integrally with the spool.
In a first aspect of the neutral position holding mechanism of the invention, a positioning member of a nearly same width as the spool operating member is disposed in the casing, and both the positioning member and the spool operating member are clamped from both sides by a pair of pressing members receiving biasing forces in mutually opposite directions, so that the spool operating member is held at a position corresponding to the neutral position of the movable swash plate. Thus, in a simple and small structure, as for neutral position regulation, the neutral position holding mechanism capable of adjusting the position of the positioning member is presented.
In the first aspect of the neutral position holding mechanism, the pressing member receives a spring biasing force, and serves as a spring retainer free to move forward or backward with respect to the positioning member, and it is no longer necessary to receive the spring biasing force with a stop ring or other additional member, that is, risk of dislocation of stop ring is eliminated, so that the durability is enhanced. At the same time, the precision of neutral position holding is enhanced.
Receiving the spring biasing force, this pressing member works as a spring retainer that is free to move forward or backward with respect to the positioning member.
Constituent members of the neutral position holding mechanism also include a rod having this positioning member, and the pressing member is disposed movably along the axial center direction of the rod, and a step abutting against the pressing member is formed in the rod so as to define the move of the pressing member in a direction remote from the positioning member by resisting the biasing force, so that the rotation control mechanism is composed. As a result, the maximum rotating angle of the movable swash plate from the neutral position can be accurately set, the durability is improved and a high precision can be maintained for a long period. Besides, since the position precision of the step is determined by the mechanical processing precision when machining the rod, it is not necessary to adjust the rotation control mechanism after assembling the rod into the casing and adjusting the neutral position, and therefore, for example, the adjusting step before shipping can be omitted.
In the neutral position holding mechanism, usually, the rod is fixed in position, and when adjusting the position of the positioning member at the time of clamping at both pressing members by the biasing force from both sides, the rod can be moved in the axial center direction by operation from outside of the casing. Therefore, the neutral position can be adjusted only by operating the rod without having to disassemble the neutral position holding mechanism, so that the neutral position can be adjusted easily.
The casing is filled with fluid, and in each spring retainer, an orifice may be formed for passing fluid between the disposing space of each spring and the disposing space of the positioning member. By this orifice, a damper action can be obtained when manipulating the manual operation member. That is, when the manual operation member is handled slowly, the manual operation member can be turned with a small effort, and the slant angle of the movable swash plate can be manipulated. When the manual operation member is moved suddenly, a large force is required to turn the manual operation member, and it is hard to manipulate the slant angle of the movable swash plate, so that occurrence of shock due to sudden operation of the manual operation member can be suppressed.
Alternatively, the neutral position holding mechanism can be formed integrally as a cartridge, and may be detachably installed in the casing. This configuration facilitates adjustment of neutral position and maintenance of the neutral position holding mechanism. Further, the neutral position holding mechanism can be reduced in size, and the cost is much lowered.
In a second aspect of the neutral position holding mechanism of the invention, the casing is filled with pressure fluid, and a solenoid proportional valve is disposed in the casing, so that the move of the spool operating member may be controlled by the supply control of pressure fluid to the neutral position holding mechanism by the solenoid proportional valve. That is, as the hydraulic servo mechanism for controlling the swash plate angle for enabling automatic control, hydraulic control of the neutral position holding mechanism is utilized. Therefore, in addition to manual operation, the hydraulic servo mechanism having an electronic control function realizing control of higher precision can be assembled in a compact design. Still more, for the hydraulic control valve serving as automatic swash plate control mechanism which does not drive directly the spool of the hydraulic servo mechanism as in the prior art but requires only a capacity enough for hydraulic control of spool operating member through the neutral position holding mechanism, a solenoid proportional valve of commercial class can be used, so that the cost can be saved. If either the manual operating mechanism or electronic control function fails to operate due to trouble or other cause, the operation can be continued by the other one.
For a first example of the neutral position holding mechanism of the second aspect which moves the spool operating member as being controlled by the solenoid proportional valve, in the casing, a piston fitting the spool operating member is disposed and a pair of biasing members are disposed therein at both sides of the piston respectively. The piston is held by the biasing forces of the pair of biasing members from both sides so as to hold the spool operating member at a position corresponding to the neutral position of the movable swash plate. A pair of the solenoid proportional valves are provided so as to control supply of pressure fluid to the respective hydraulic chambers at both sides of the piston.
Further, for a second example of the neutral position holding mechanism of the second aspect which moves the spool operating member as being controlled by the solenoid proportional valve, in the casing, a piston fitting the spool operating member is disposed, a biasing member is disposed at one side of the piston, and a hydraulic chamber is formed at the other side of the piston. The sole solenoid proportional valve controls the supply of pressure fluid to the hydraulic chamber. Therefore, the piston is held by equilibrium between the biasing force of biasing member at one side and the oil pressure of the pressure fluid at the other side, so that the spool operating member may be held at a position corresponding to the neutral position of the movable swash plate.
Moreover, guide means may be provided to prevent the piston from turning and guide the piston so as to move only along its axial center direction. As a result, moment is not applied to a pin serving as the spool operating member from the piston, and friction can be reduced in the portion of the pin contacting with other member on the outer circumference, so that the pin may slide smoothly.
The spool operating member such as a pin may be disposed integrally with the piston. In this case, it is effective to eliminate deviation in the sliding direction occurring in the fitting parts of the piston and pin or deviation due to rotation around the axis, and hence the transmission efficiency of operating force is enhanced. By integrating the pin and piston, further, the strength as a rigid body is also heightened.
The hydraulic servo mechanism in a configuration for hydraulically controlling the spool operating member by the solenoid proportional valve through such neutral position holding mechanism is used for controlling both the movable swash plate angles of the hydraulic pump and hydraulic motor in the case that the hydraulic pump and hydraulic motor of the hydraulic continuously variable transmission are both of variable displacement type. A wide speed variable range of the hydraulic continuously variable transmission is assured, and control of high precision is realized.
These and other objects, features and effects of the invention will be fully apparent from the following description taken in conjunction with the accompanying drawings.